Both IIpo Huhtaniemi's and our group recently succeeded in generating LH receptor knockout mice by gene targeting in embryonic stem cells. Although this gene knockout was not lethal, it rendered animals infertile. While ovaries of wild- type and heterozygous animals contained LH receptors, ovaries of homozygous littermates contained none. Also, while ovaries of wild-type and heterozygous animals were normal in size and contained preovulatory follicles and corpora lutea, the ovaries of homozygous littermates were small and pale with an arrest of follicular growth at the antral stage. Preliminary studies indicated this arrest could, at least partly, be due to a decrease in telomerase levels and a consequent increase in apoptosis. In homozygous animals, LH levels were markedly elevated, FSH levels were moderately elevated, and estradiol and progesterone levels decreased but were not totally suppressed. Knockout animals can be extremely useful in answering a number of unknowns in LH biology. For example, we could learn: 1) whether LH actions are required for the presence of normal numbers of primordial, primary, preantral and antral follicles; 2) whether FSH can induce follicular growth and ovulation in the total absence of LH actions; 3) what role LH signaling plays in ovarian development and function from one week after birth through one year of age; 4) what ovarian actions of LH are mediated by estradiol, progesterone and testosterone; 5) identify and characterize previously unidentified ovarian genes that are regulated by estradiol, progesterone, testosterone, LH or by their combination; and 6) whether using gene therapy to introduce LH receptors into ovaries of null animals makes them cyclic and ovulate but still not get pregnant because they do not have LH receptors in the uterus. These are only a few examples of how the use of null animals could advance our current understanding on the role of LH in different ovarian functions. We propose three specific aims in this application: 1) Investigate structural and functional defects in ovaries of 7-day, 25-day, 60-day and 1-year old null mice to compare with their age- matched, wild-type and heterozygous siblings. 2) Investigate whether estradiol, progesterone and testosterone replacement therapy can correct structural and functional defects in ovaries of LH receptor knockout animals. 3) Determine whether retroviral mediated LH receptor gene transfer can correct structural and functional defects in ovaries of null animals so they become cyclic and ovulate even though pregnancy may not occur due to the absence of LH receptors in the uterus. There are several strengths in this proposal. Foremost is studying LH biology using knockout technology. Second is using steroid hormone replacement and gene therapies. Third is using cDNA expression arrays, a powerful technique in gene expression analysis. All techniques to be used in the proposed studies have already been established to obtain preliminary data presented in the proposal.